//输出num！:例 3! = 1 + 2 + 3

import java.util.Scanner;

public class sumAdd {
    public static int Sum(int num)
    {
        if(num != 0)
            return num + Sum(num - 1);
        return num;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        System.out.println(Sum(num));
    }
}
